This invention relates to an intake system for engines, and more particularly to an induction system that offers significantly improved low and medium speed performance for the engine.
The difficulties in achieving good charging efficiencies at low engine speeds and when the throttle valve of the engine is partially or fully closed are well known. Under such conditions the uneven intake stroke of the engine causes intermittent flow through the induction passage which gives rise to the poor charging efficiency and low engine performance. Recently, it has been proposed to offset this deficiency and improve breathing capacity under these conditions by providing a plenum chamber that communicates with the intake passage downstream of the throttle valve. Several embodiments of such constructions and a more thorough description of the advantages and theory behind this system are disclosed in the copending application of Noritaka Matsuo, et al. entitled "Intake System for Engine," Ser. No. 163,201, filed June 25, 1980, and assigned to the assignee of this application. With an induction system embodying a plenum chamber of this type, the fuel and air charge delivered to the plenum chamber after the completion of one intake stroke may not be completely discharged back into the induction system during the next succeeding intake stroke under all running conditions. As a result of the retention of a portion of the fuel air charge in the plenum chamber during succeeding intake cycles, there may be fuel condensation occur within the plenum chamber. The condensed fuel will eventually reenter the induction system through the connecting passage, but the degree of such reentry is variable and can, under some circumstances result in mixture strength variations being delivered to the engine chambers.
In order to preclude these mixture strength variation problems while maintaining the advantages of the use of such a plenum chamber, it has been proposed to orient the plenum chamber and its connecting passage with the induction system in such a way that any condensed fuel will be fed continuously to the induction system. This can be done by providing the plenum chamber with an inclined lower wall which terminates at the conduit that communicates the plenum chamber with the intake system. Embodiments of such an arrangement are shown in the copending application of Noritaka Matsuo, et al., entitled "Intake System for Engines," Ser. No. 238,641, filed Feb. 26, 1981. In many instances it may be impossible, due to physical environment in which the engine and induction is employed, to make use of such an arrangement where the fuel is returned to the intake system from the plenum through the same conduit that communicates the air and fuel between the plenum chamber and the intake system. This is particularly true in conjunction with motorcycles wherein spacial limitations are at a premium.
It is, therefore, a principal object of this invention to provide an improved intake system for internal combustion engines.
It is another object of this invention to provide an improved intake system for engines for significantly augmenting low and medium speed charging efficiencies.
It is yet a further object of this invention to provide an engine induction system including a plenum chamber device and an improved arrangement for ensuring against variations in mixture strength during engine running.